Membrane light modulator

ABSTRACT

A collodion membrane coated with a plurality of spaced apart, reflective and conductive strips is stretched across a glass plate having an array of holes. The holes are arranged in rows and columns. Each strip is located over one row of holes. A separate electrode is located underneath each column of holes. Electric signals applied to the strips and electrodes produce electrostatic deflections in the portions of the membrane above the holes; the deflection over any one hole being dependent on the signal applied to the strip above the hole and the signal applied to the electrode below the hole. In use a beam of light striking the strips on the membrane is reflected and at the same time phase modulated.

United States Preston, Jr. et al.

[ MEMBRANE LIGHT MODULATOR [75] Inventors: Kendall Preston, Jr., NewHaven;

Julian Wasserman, Norwalk; Edward T. Siebert, Danbury, all of Conn.

[73] Assignee: The Perkin-Elmer Corporation,

Norwalk, Conn.

[22] Filed: Dec. 26, 1968 [21] Appl. No.: 786,926

1 Mar. 12, 1974 3,479,109 11/1969 Preston 350/161 FOREIGN PATENTS ORAPPLICATIONS 822,866 10/1937 France 350/161 Primary Examiner-Ronald L.Wibert Assistant ExaminerV. P. McGraw Attorney, Agent, or Firm-John K.Conant [5 7] ABSTRACT A collodion membrane coated with a plurality ofspaced apart, reflective and conductive strips is stretched across aglass plate having an array of holes. The holes are arranged in rows andcolumns. Each strip is located over one row of holes. A separateelectrode is located underneath each column of holes. Electric signalsapplied to the strips and electrodes produce electrostatic deflectionsin the portions of the membrane above the holes; deflection over any onehole being dependent the sigr/al applied to the strip above the hole andthe si-gnafapplied to the electrode below the hole. In use a beam oflight striking the strips on the membrane is reflected and at the sametime phase modulated.

I 5 Claims, 3 Drawing Figures PATENTED UAR I 2 I974 h z M 07 mg? m 5 1mmm n z w Z d n M W I 34 W MEMBRANE LIGHT MODULATOR This inventionrelates to light modulators. More particularly, this invention relatesto light modulators in which the surface contour of a deformablereflective element or medium is selectively altered by electrical orelectromagnetic signals so as to spatially phase modulate a beam oflight impinging on the deformable surface and reflected therefrom.

Light modulators of this type are now well known in the art and commonlyused in optical communication systems, display systems, televisionsystems and a variety of other applications where modulating the phaseof a beam of light spatially (and/or temporally) is either desired orrequired. In the book Television, The Electronics of Image Transmissionin Color and Monochrome, Second Edition, V. K. Zworken and G. A. Morton,Copyright 1940 and 1954, John Wiley and Sons, Inc.; New York, on pages284-287 there is described a light modulator in which the deformablemedium is a reflective coated viscous film. The film is supported on aglass disc and is scanned by a modulated electron beam which producescorresponding changes in the thickness and hence, the contour of thefilm surface. In British Patent 778,376 to .l. H. Jeffree, there isdisclosed another light modulator of this general type. Severaldifferent embodiments are shown. In all embodiments electrostaticcharges set up in a support member cause an electrostatic attraction ofa reflective and conductive film resting on top of the support member.In US. Pat. Nos. 3,479,109 dated Nov. 18, 1969 and 3,463,572 dated Aug.26, 1969 to the assignee of this application, there is disclosed a lightmodulating device of this general type in which localized deflections ina reflective and conductive coated membrane are produced by establishingindividual isolated electrostatic charges in the wells of the supportmember on which the membrane rests.

It is an object of this invention to provide a new and improved lightmodulator.

It is another object of this invention to provide a new and improvedmembrane type light modulator.

It is still another object of this invention to provide a lightmodulator which can be used to spatially and/or temporally phasemodulate a beam of light.

It is yet still another object of this invention to provide a new andimproved technique for producing calized deflections in a membrane.

It is another object of this invention to provide a technique forproducing localized electrostatic deflections in a membrane in which thenumber of different deflections produced is much greater than the numberof different electrical signal sources used to produce the electrostaticcharges.

The above and other objects are achieved by constructing a lightmodulator according to this invention. The light modulator includes arigid nonconductive member having an array of holes. The holes arearranged in rows and columns. Located underneath each row of holes is anelectrode. The light modulator further includes a nonconductive membranestretched across the top of the rigid nonconductive member. A pluralityof spaced apart reflective and conductive strips are formed on themembrane. Each strip is positioned so as to extend over one column ofholes. Deflections in the membrane are produced by applying electricsignals to the conductive strips on the membrane and the electrodesunderneath the rigid nonconductive member. The deflections occur at theportions of the membrane and reflective strips thereon extending overthe holes and thereby phase modulate portions of a beam of lightreflected from the portions of the reflective strips over the holes. Theparticular deflection at any one hole is dependent solely on the signalapplied to the conductive strip on the membrane above the hole and thesignal on the electrode underneath the hole. One feature of theinvention is that different or independent deflections over n holes canbe realized by using only 2n voltage sources. Another feature of theinvention is that the deflections on the membrane are extremelylocalized.

Other features and advantages of the invention will become apparent onreading the following detailed description taken in connection with theaccompanying drawings in which like reference characters represent likeparts and wherein:

FIG. 1 is a perspective view ofa light modulator con structed accordingto this invention,

FIG. 2 is a section view of the light modulator of FIG. 1 taken alonglines 22, and

FIG. 3 is a section view of the light modulator of FIG. 1 taken alonglines 33.

Referring now to the drawings, there is shown a light modulatordesignated by reference numeral 11.

The light modulator 11 includes a plate 12 having an array of holes.Theplate 12 is made of rigid nonconductive material such as glass. Theholes are aligned in rows and colums. In order to identify the differentrows and columns in the drawings, the rows are labeled A, B, C, D, E andF and the columns are labeled I, II, III, IV, V and VI. Additionally,the holes in row B are numbered 201, 202, 203, 204, 205 and 206 and theholes in column III are numbered 103, 203, 303, 403, 503

and 603. Each hole is in one row and one column. For

example, hole 203 lies. in row B and column Ill. Located underneathplate 12 is a plurality of electrodes 13 through 18. Each electrode ispositioned so that it passes underneath one row of holes. For example,electrode 14 passes underneath row B. The light modulator 11 furtherincludes a set of voltage sources 21 through 26. Each voltage source isconnected to a different electrode. Plate 12 and electrodes 13 through18 rest on a support member 27 of nonconductive material such as glass.Stretched across the top surface of plate 12 is a thin membrane 31 ofcollodion or other similar nonconductive deformable material. Themembrane 31 is coated with a plurality of spaced apart reflective andconductive strips 32 through 37. The strips are arranged so that eachstrip is located over one column of holes. Thus, as can be seen in thedrawing, strip 34 extends over column Ill. The light modulator 11further includes a second set of voltage sources 41 through 46. Eachvoltage source is connected to a separate strip. Deflections in themembrane 31, and hence deflections of the reflective portions thereof,are produced by activating the voltage sources. The deflections, whichare electrostatically induced, are confined to those portions of themembrane 31 directly above the holes. The amount of deflection of themembrane 31 over any one hole is dependent on the voltage signal on theconductive strip extending over any particular hole and the voltagesignal on the electrode located underneath the hole. If the signals ared.c., the deflection is dependent on their potential difference. If thesignals are a.c., the

deflection is dependent on their potential difference and also on theirsum and difference frequencies. Thus, for example, the deflection of theportion of the membrane extending over hole 403 is dependent on voltagesources 24 and 43.

By the proper selection of voltage sources, it is possible to obtain adifferent deflection of the membrane at each hole. One convenienttechnique for achieving this is by having all the voltage sourcesdifferent (in size if do. or size and/or frequency if a.c.) and byhaving all the voltage sources in one set different multiples of onediscrete unit more than the largest voltage source in the other set. Forexample, voltage sources 21 through 26 could be 1 through 6 volts d.c.(in any order) and voltage sources 41 through 46 could be 7, 14, 21, 28,35 and 42 volts d.c. (also in any order). If a.c. signals are used, thedifference need only be in terms of frequencies. For example, one set ofvoltages could be 10, 20, 30,40, 50 and 60 cycles a.c. and the other set70, 140, 210, 280, 350 and 420 cycles a.c.

It is to be understood that the number of rows and columns shown in thedrawings is only by way of illustration and for simplicity. In actualpractice, each row and column may contain as many as several hundredholes.

another alternative arrangement, the electrodes 13' through 18 could belocated underneath the substrate 27 and electrically connected toindividual electrodes located in each hole.

Obviously, many other alterations and modifications will become apparentto those skilled in the art. It is, therefore, to be understood that thescope of this invention is as defined in the appended claims.

What is claimed is:

l. A light modulator for use in modulating the phase of a beam of lightincident thereon comprising? a. a rigid plate of nonconductive materialhaving an array of holes arranged in rows in one direction and columnsin another direction;

b. a plurality of electrodes located underneath the plate, eachelectrode passing underneath one column of holes;

c. a nonconductive membrane stretched across the top of the plate;

(1. a plurality of spaced apart reflective and conductive strips on saidmembrane, arranged so that each strip passes over one row of holes onthe plate;

e. means connecting voltage sources to the strips for establishing adifferent electric charge on each of the strips; and

f. means connecting voltage sources to the electrodes for establishing adifferent electric charge on each of the electrodes;

whereby the deflection of the membrane in the vicinity of each hole isdependent solely on the electric charge on the electrode underneath thehole and the electric charge on the strip on the membrane above thehole.

2. The invention according to claim 1 and wherein the membrane is madeof collod'ion.

3. The invention according to claim 1 and wherein the columns and rowsare in straight lines and the columns are at right angles relative tothe rows.

4. The invention according to claim 1 and wherein the electricsignals'applied to each electrode and each strip are different.

5. The invention according to claim 4 and wherein the electric signalapplied to each electrode is a different frequency and the electricsignal applied to each strip is a different multiple of a frequencygreater than the highest frequency applied to any one of the electrodes.

1. A light modulator for use in modulating the phase of a beam of lightincident thereon comprising: a. a rigid plate of nonconductive materialhaving an array of holes arranged in rows in one direction and columnsin another direction; b. a plurality of electrodes located underneaththe plate, each electrode passing underneath one column of holes; c. anonconductive membrane stretched across the top of the plate; d. aplurality of spaced apart reflective and conductive strips on saidmembrane, arranged so that each strip passes over one row of holes onthe plate; e. means connecting voltage sources to the strips forestablishing a different electric charge on each of the strips; and f.means connecting voltage sources to the electrodes for establishing adifferent electric charge on each of the electrodes; whereby thedeflection of the membrane in the vicinity of each hole is dependentsolely on the electric charge on the electrode underneath the hole andthe electric charge on the strip on the membrane above the hole.
 2. Theinvention according to claim 1 and wherein the membrane is made ofcollodion.
 3. The invention according to claim 1 and wherein the columnsand rows are in straight lines and the columns are at right anglesrelative to the rows.
 4. The invention according to claim 1 and whereinthe electric signals applied to each elecTrode and each strip aredifferent.
 5. The invention according to claim 4 and wherein theelectric signal applied to each electrode is a different frequency andthe electric signal applied to each strip is a different multiple of afrequency greater than the highest frequency applied to any one of theelectrodes.